1. Field of the Invention
The present invention relates to an electrode material, an electrode, and a lithium ion battery, and particularly to an electrode material that is preferably used for battery cathode materials, furthermore, lithium ion battery cathode materials, an electrode containing the above-described electrode material, and a lithium ion battery including a cathode made of the above-described electrode.
2. Description of Related Art
In recent years, as a battery expected to procure a decrease in size and weight and an increase in capacitance, non-aqueous electrolytic solution secondary batteries such as lithium ion batteries have been proposed, and have been put into practical use.
The lithium ion battery is made up of a cathode and an anode which can reversibly accept and expel lithium ions and a non-aqueous electrolyte.
Regarding anode materials of lithium ion batteries, generally, a carbon-based material or a Li-containing metallic oxide which can reversibly accept and expel lithium ions, such as lithium titanate (Li4Ti5O12), is used as an anode active material.
On the other hand, regarding cathode materials of lithium ion batteries, a Li-containing metallic oxide which can reversibly accept and expel lithium ions, such as lithium iron phosphate (LiFePO4) or an electrode material mixture containing a binder and the like is used as a cathode active material. In addition, a cathode of a lithium ion battery is formed by applying the electrode material mixture on a surface of a metal foil called a collector.
The lithium ion battery has a light weight, a small size and a high energy compared to secondary batteries of the related art, such as lead batteries, nickel-cadmium batteries and nickel-hydrogen batteries, and therefore the lithium ion battery is used not only in small-scale power supplies in portable electronic devices such as mobile phones and notebook personal computers but also in large-scale stationary emergency power supplies.
In addition, in recent years, studies are being made regarding the use of the lithium ion battery as high-output power supplies in plug-in hybrid vehicles, hybrid vehicles, electromotive tools and the like, and, for batteries being used in those high-output power supplies, a high-speed charge and discharge characteristic is required.
However, there is a problem in that an electrode active material, for example, an electrode material containing a lithium phosphate compound which can reversibly accept and expel lithium ions has a low electron conductivity. Therefore, in order to increase the electron conductivity of electrode materials, an electrode material is proposed in which the surfaces of particles of an electrode active material are coated with an organic compound which serves as a carbon source, and then the organic compound is carbonized, whereby a carbonaceous coat is formed on the surface of the electrode active material, and carbon in the carbonaceous coat between the surfaces of particles of an electrode active materials as an electron-conducting material (see Japanese Laid-open Patent Publication No. 2001-15111).